Surface grinding machine and method for adjusting a surface grinding machine

ABSTRACT

The present disclosure relates to a surface grinder having at least one grinding tool, a workpiece holder for holding at least one workpiece, a drive unit for driving the workpiece holder in a rotational direction and a clutch device that provides a rotationally fixed connection between the drive unit and the workpiece holder that can be released at a specifiable limit torque.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of provisional application Ser. No.61/185,845, filed on Jun. 10, 2009, the contents of which areincorporated herein by reference in their entirety.

FIELD

The present disclosure relates to a surface grinder.

BACKGROUND

For surface grinders, a workpiece holder is used to bring the workpieceheld on a workpiece holder into engagement with at least one grindingtool. It is necessary in this respect to be able to fix the workpiecewith high precision on the workpiece holder, so that when the workpieceis introduced into the machining area of the grinding tool, theworkpiece holder and the grinding tool do not tilt with respect to oneanother. A correspondingly careful matching is necessary in the area ofa workpiece exit from the machining area, in order to avoid tiltingbetween the workpiece, the workpiece holder, the grinding tool and anoutlet guide adjoining the machining area.

A transfer of non-machined workpieces from a loading machine intoworkpiece receptacles of the workpiece holder is also critical. In thisarea as well, if all components are not precisely matched, it ispossible for a workpiece to become tilted with respect to thesecomponents. All of this implies that a surface grinder must be set upextremely carefully to avoid damage to components of the surface grinderand/or workpieces.

SUMMARY

Starting from this situation, the present disclosure is based on theproblem of preventing damage to a surface grinder.

This problem is solved according to the present disclosure for a surfacegrinder of the type mentioned above by a clutch device that provides arotationally fixed connection between the drive unit and the workpieceholder that can be released at a predetermined limit torque.

The surface grinder according to the present disclosure makes itpossible to release a rotationally fixed connection between the driveunit and the workpiece holder as a function of a specifiable limittorque. This makes it possible to exert the drive torque necessary forsurface-grinding of a workpiece, but with the rotationally fixedconnection being released when a limit torque is reached. Theconsequence is that the drive unit can be decoupled from the workpieceholder and damage to the surface grinder of the type mentioned above canbe prevented. As soon as the specifiable limit torque is exceeded, therelease of the rotationally fixed connection of the drive unit and theworkpiece holder prevents the workpiece holder from being driven furtherin the direction of rotation in a state where it is tilted with respectto a workpiece and/or other components of a surface grinder.

The surface grinder according to the present disclosure is particularlyadvantageous if a disk-shaped workpiece holder is used, the overallheight of which is at most approximately 1 cm or even only a fewmillimeters. Such a thin workpiece holder has the advantage of beingable to machine very thin workpieces, but it has the disadvantage of theworkpiece holder itself having very low distortion resistance. Since theworkpiece holders, with a diameter of about 50-100 cm or even more,extend over a very large area in comparison to their thickness, they areparticularly susceptible to a deformation based on the tilting of aworkpiece holder with respect to a workpiece and/or other parts of thesurface grinder.

Due to the separability of the rotationally fixed connection between theworkpiece holder and the drive unit, and the accompanying stoppage ofthe workpiece holder, additional components of the surface grinder canalso be protected against damage in the area of a workpiece feeder and aworkpiece discharge unit. The same applies to the protection of anoptional loading unit by means of which the workpiece holder can befurnished with non-machined workpieces. In this way, a device formeasuring the geometry of a machined workpiece that may be present inthe vicinity of the workpiece holder can also be protected from damage.

The surface grinder according to the present disclosure also makes itpossible to set up the machine with a less of an exacting effort andwith higher tolerances.

Within the scope of the present disclosure, it is possible for thespecifiable limit torque to be set manually, based on empirical values,for example. It is preferred, however, that a control unit is providedwhich adjusts the limit torque of the clutch device as a function of anactually occurring maximum drive torque. It is also preferred that thelimit torque is set to be higher than the actually occurring maximumdrive torque in order to prevent an unintended release of therotationally fixed connection.

The clutch device in one form is constructed in the form of anelectromagnetic clutch. This carries the advantage of being able toadjust the limit torque very precisely.

It is further preferred that the rotationally fixed connection is africtionally engaged connection. Thereby, the mechanical stress onengaged clutch elements can be reduced.

The surface grinder in one form is constructed as a double surfacegrinding machine that has two grinding tools, between which a grindinggap is formed in which a workpiece can be machined on opposite workpiecesurfaces. The present disclosure further relates to a method for settingup a surface grinder, wherein the surface grinder comprises at least onegrinding tool, a workpiece holder for holding at least one workpiece anda drive unit for driving the workpiece holder in a rotational direction.

The present present disclosure is based on the additional problem ofcreating a method for setting up a surface grinder with which damage tothe surface grinder can be prevented.

This problem is solved according to the present disclosure for a methodas mentioned above in that the actually occurring maximum drive torqueis determined during the grinding of at least one sample workpiece, andin that a rotationally fixed connection that can be released at a limittorque determined as a function of the maximum drive torque is producedbetween the drive unit and the workpiece holder.

Advantages and various forms of the method according to the presentdisclosure have in part already been explained above in connection withthe advantages and forms of the surface grinder according to the presentdisclosure. Therefore only those advantages and forms of the methodaccording to the present disclosure will be discussed that were notalready explained above in connection with the advantages and forms ofthe surface grinder according to the present disclosure.

By determining an actually occurring maximum drive torque using at leastone sample workpiece, the drive torques occurring during the regularoperation of the surface grinder can be determined precisely and simply.The limit torque, which is then to be specified for the regularoperation of the surface grinder, is determined as a function of theactually occurring maximum drive torque.

One possibility for determining the actually occurring maximum drivetorque is to detect the power requirements of the drive unit. Forexample, voltage or current values at which the drive unit is operatedcan be detected.

Additionally or alternatively, it is possible to measure the actuallyoccurring maximum drive torque with a torque measuring device. Such ameasurement device is preferably arranged in a spatial connection withthe clutch device, for example, between the drive unit and the clutchdevice or between the clutch device and the workpiece.

It is further preferred if the limit torque is equal to the maximumdrive torque multiplied by a factor greater than 1. In this way it canbe assured that a slight exceeding of the maximum drive torque measuredusing the sample workpiece does not lead to an undesired disengagementof the clutch device in the regular operation of the surface grinder.

The limit torque is preferably equal to the maximum drive torquemultiplied by a factor of less than roughly 1.5. In particular, thefactor is between approximately 1.1 and approximately 1.3. These factorsoffer a good compromise between an overload protection of the surfacegrinder components and an operation which is as free of interruption aspossible.

It is further preferred that at least one sample workpiece with the samegeometry as a non-machined workpiece should be surface-ground by meansof the surface grinder. Thereby the actually occurring maximum drivetorque can be determined very precisely. In this context, it isadvantageous if maximum drive torques determined using sampleworkpieces, and possibly the associated limit torques are stored, sothat these values are already known and can be used after a re-setup ofthe surface grinder.

The maximum drive torque is advantageously determined when an engagementsurface area between the at least one grinding tool and the at least onesample workpiece is at a maximum. In this state of the surface grinder,the friction surfaces between the workpiece and the grinding tool aremaximized so that maximum drive torques appear in this state. If aplurality of workpieces is simultaneously machined in the machiningarea, the maximum drive torque and thus the limit drive torque areincreased correspondingly.

DRAWINGS

In order that the disclosure may be well understood, there will now bedescribed various forms thereof, given by way of example, referencebeing made to the accompanying drawings, in which:

FIG. 1 shows a top view of one form of a surface grinder;

FIG. 2 shows a side view of the surface grinder according to FIG. 1, inwhich a drive unit and a clutch device are represented; and

FIG. 3 shows a side view of the clutch device according to FIG. 2, alonga cross section labeled II-II in FIG. 2.

DETAILED DESCRIPTION

One form of a surface grinder, denoted overall by reference number 10 inFIG. 1, is constructed as a double surface grinder and comprises twogrinding disks, of which an upper grinding disk 12 is indicated bydashed lines in FIG. 1. The upper grinding disk 12 and the lowergrinding disk can each be driven in rotation about a grinding disk shaft14.

The surface grinder 10 further comprises a disk-shaped workpiece holder16 which is rotatably drivable about a workpiece holder shaft 18. Theworkpiece holder shaft 18 and the grinding disk shaft 14 are mutuallyparallel or are inclined relative to one another by a few degrees, atmost 5° for example.

The workpiece holder 16 comprises a plurality of workpiece receptacles20, which are preferably spaced identically in the radial directionrelative to the workpiece holder shaft 18 and are furthermore spacedpreferably equally from one another in the circumferential direction.

The workpiece holder 16 comprises at least two, and in particular atleast ten workpiece receptacles 20. A workpiece receptacle 20 can beformed, for example, by a hole-shaped recess, which serves to receive aworkpiece. A workpiece 22 is shown crosshatched in FIG. 1 for clarity.

The surface grinder 10 has a loading area 24 in which non-machinedworkpieces 22 can be inserted into a workpiece receptacle 20. Theinsertion can be done manually or by means of a loading device 26, whichin particular has a magazine 28 for storing non-machined workpieces 22.

The surface grinder 10 further comprises a machining area 30 in whichworkpieces 22 held on workpiece holder 16 are engaged with the uppergrinding tool 12 and the lower grinding tool for surface grinding.

The surface grinder 10 further comprises a removal area 32 in whichworkpieces 22 can be removed from the workpiece receptacles 20.

In the machining area 30, the upper grinding tool 12 and the lowergrinding tool are spaced away from one another in such a manner that agrinding gap results in which workpieces 22 are accommodated andsupported at the top and the bottom relative to the direction ofgravity. Outside the machining area 30, the workpieces 22 are supportedin the loading area 24 and in the removal area 32 on their undersidewith the aid of workpiece rests not shown in the drawing.

The surface grinder 10 comprises a measurement device 34 that isarranged in an entry area of the removal area 32. A thickness of aworkpiece 22 parallel to the extension direction of the grinding gap ismeasured with the aid of the measurement device 34.

Adjoining the machining area 30, the surface grinder 10 has a firstguide unit 36 in the vicinity of an inlet to the machining area 30, anda second guide unit in the vicinity of an outlet of the machining area30. The guide units 36 and 38 each have a plate-shaped guide element 40,42 which has a guide surface 44, 46, respectively, facing the workpieceholder 60. The guides 44, 46 are each finished with a border 48 or 50respectively.

Non-machined workpieces 22 can be pressed with the aid of the guideelement 40 of the first guide unit 36 downwards relative to thedirection of gravity against a workpiece rest (not shown), so that aworkpiece can be oriented precisely relative to the direction of gravitybetween the upper grinding tool 12 and the lower grinding tool. In acorresponding manner, a machined workpiece 22 can be guided out of themachining area 30 with the aid of the guide element 42 of the secondguide unit 38.

In the removal area 32, the surface grinder 10 further comprises aworkpiece discharge element 52, which is constructed in the form of aslide. Finished machined workpieces 22 held on the workpiece holder 16can be removed downwards out of the workplace receptacles 20 anddischarged via the workpiece discharge element 52.

A drive unit 56, which is embodied, in particular, in the form of anelectric motor, is provided for driving the workpiece holder 16 aboutthe workpiece holder axis 18 in the direction of rotation 54.

The drive unit 56 does not act directly on the workpiece holder 16, butrather through the interposition of a clutch device 58. In an engagedstate, the clutch device 58 provides a rotationally fixed connectionbetween the drive unit 56 and the workpiece holder 16. The rotationallyfixed connection of the clutch device 58 is released as a function of apredetermined limit torque.

The limit torque of the clutch device 58 is controlled using a controlunit 60, which preferably also communicates with the drive unit 56 inorder to specify an energy requirement of the drive unit 56.

The clutch device 58 is preferably constructed in the form of anelectromagnetic clutch 62, which is shown in greater detail in FIG. 3.

An input torque of the drive unit 56 is transferred with the aid of aninput shaft 64 to a friction liner support 66. The friction linersupport 66 has a friction liner receptacle 68 in which, in particular,an annular friction liner 70 is accommodated. The friction liner 70 ismovable axially relative to the workpiece holder shaft 18. On itsperipheral surface, the friction liner 70 has teeth 72 which create apositively engaged connection in the direction of rotation with matchingteeth of the friction liner receptacle 68.

The friction liner 70 can be magnetized, so that it can be attracted byan annular electromagnet 74. The electromagnet 74 is rotationally fixedto an electromagnet holder 16 into which a coil (not shown in detail) isintegrated, said coil can be electrically connected with the aid of aterminal 78. When the coil is energized, the electromagnet 74 generatesa magnetic field that presses the friction liner 70 against theelectromagnet 74, so that a fictional engagement between these partnersresults. The intensity of the frictional engagement is dependent on thepower applied to the electromagnet 74 as specified by means of thecontrol unit 60.

The magnet support 76 is rotationally fixed to an output shaft 80, whichis rotatably seated by means of rolling-contact bearings 82 in astationary housing 84.

The output shaft 80 is rotationally fixed at its end remote from theclutch device 58 to a workpiece support 86. Said end of the output shaft80 is additionally connected to a bolt 88 that penetrates a centralcutout of the workpiece holder 16. This bolt cooperates with a clampingsleeve 90, with which a clamping socket 92 can be pressed down fromabove onto the workpiece holder 16.

Annular spacer elements 94, which allow an adaptation to differentthicknesses of different workpiece holders 16, are arranged between theworkpiece holder support 86 and the underside of the workpiece holder16.

The workpiece holder 16 is rotationally fixed between the spacerelements 94 and the clamping socket 92.

To set up the surface grinder 10 it is possible to use eight sampleworkpieces, for example, which are brought into the machining area 30 insuch a manner that they are simultaneously engaged with the uppergrinding tool 12 and the lower grinding tool. A drive torque of thedrive unit 56 necessary to transport the sample-grinding tools iscorrelated with the energy requirement of the drive unit 56. From this,a maximum occurring drive torque can be calculated, which is thenmultiplied by a factor of, for example, between approximately 1.1 andapproximately 1.3. This yields a limit torque which can be adjustedusing the control unit 60 on the clutch device 58 by appropriateapplication of power to the electromagnet 74.

Then non-machined workpieces 22 can be fed to the workpiece holder 16from the loading device 28 and introduced into the machining area 30.After the machining of the workpieces they are guided out of themachining area 30 by further movement of the workpiece holder 16 in therotational direction 54, so that they can be removed from the workpieceholder 16 in the removal area 32.

It is possible for the workpiece holder 16 to be operated in steps or torotate continuously.

If a workpiece 22 becomes tilted during the operation of the surfacegrinder 10, for example in the vicinity of the outlet of the magazine 28in the direction towards the workpiece holder 16, or in the vicinity ofthe border 48 of the first guide unit 36, or in the vicinity of theborder 50 of the second guide unit 38, this causes the limit torque tobe exceeded, whereby the rotationally fixed connection of the clutchdevice 8 between the drive unit 56 and the workpiece holder 16 isreleased by slippage of the friction liner 70 on the electromagnet 74.

The above-described possibility of a tilting of a workpiece 22 is basednot only on the fact that parts of the surface grinder 10 may not be setup precisely, but also on the fact that workpieces 22 in the machiningarea 30 may be lifted up because of the use of coolant, so that theycollide with the borders 48, 50 or with a border of the grinding tools.

In an alternative form, not shown in the drawings, the clutch device 58is arranged relative to the workpiece holder 16, on a side facing awayfrom the drive unit 56, for example, between the clamping sleeve 90 andthe clamping socket 92.

1. A surface grinder comprising at least one grinding tool, a workpieceholder for holding at least one workpiece, and a drive unit for drivingthe workpiece holder in a rotational direction, characterized by aclutch device that provides a rotationally fixed connection between thedrive unit and the workpiece holder that can be released at aspecifiable limit torque.
 2. The surface grinder according to claim 1,characterized by a control unit that sets the limit torque of the clutchdevice as a function of an actually occurring maximum drive torque. 3.The surface grinder according to claim 1, characterized in that theclutch device is constructed in the form of an electromagnetic clutch.4. The surface grinder according to claim 1, characterized in that therotationally fixed connection is a frictionally engaged connection. 5.The surface grinder according to claim 1, characterized in that thesurface grinder is constructed as a double surface grinder.
 6. A methodfor setting up a surface grinder, wherein the surface grinder comprisesat least one grinding tool, a workpiece holder for holding at least oneworkpiece and a drive unit for driving the workpiece holder in arotational direction, characterized in that an actually occurringmaximum torque during the grinding of a sample workpiece is determined,and in that a rotationally fixed connection is produced between thedrive unit and the workpiece holder that can be released at a limittorque determined as a function of the maximum drive torque.
 7. Themethod according to claim 6, characterized in that the actuallyoccurring maximum drive torque is determined by detecting the energyrequirement of the drive unit.
 8. The method according to claim 6,characterized in that the actually occurring maximum drive torque ismeasured with a torque measurement device.
 9. The method according toclaim 6, characterized in that the limit torque is equal to the maximumdrive torque multiplied by a factor greater than
 1. 10. The methodaccording to claim 6, characterized in that the limit torque is equal tothe maximum drive torque multiplied by a factor of less thanapproximately 1.5.
 11. The method according to claim 6, characterized inthat the at least one sample workpiece has the same geometry as anon-machined workpiece to be surface-ground by means of the surfacegrinder.
 12. The method according to claim 6, characterized in that themaximum drive torque is determined when an engagement surface areabetween the at least one grinding tool and the at least one sampleworkpiece is at a maximum.